Method for the production of sheets

ABSTRACT

The disclosure proposes a method for the production of sheets from the slabs cut from a bar of unkilled steel cast by the continuous casting method, wherein the cast bar, after it has solidified completely and as soon as its cross section has an equalized temperature in the range of 900* to 1,200* C., preferably 1,000* to 1,100* C., is shaped in one step so as to reduce its cross section by about 10 to 20 percent, whereupon it is shorn to length, and the slabs are then heated to rolling temperature and shaped in a plurality of passes. Owing to this method the bubble wreath which is characteristic for unkilled steel slabs is eliminated so that the heat transition from the surface to the core is improved.

United States Patent Schoffmann [451 July 25, 1972 54] METHOD FOR THEPRODUCTION OF 3,491,823 1/1970 Tarmann et al ..l64/76 SHEETS [72]lnventor: Rudolf Schoffmann, Linz, Austria OTHER PUBLICATIONS 1Assignee: Vminigte oster-reichische Eisen-und The Making Shaping andTreating of Steel, 1964. p. 550.

Stahlwerke Aktiengesellschaft, Linz, Ausi Primary E.taminer-J. SpencerOverholser [22] Filed: April 27 1970 Assistant Examiner-John E. RoethelAtmrne v-Brumbaugh. Graves, Donohue & Raymond [2]] Appl. No.: 32,230

57] ABSTRACT [30] Foreign Applicafim Prim'ity Data The disclosureproposes a method for the production of sheets May 9, 1969 Austria; ..A4445/69 l the 81-395 cm mm a bar Steel by tinuous casting method,wherein the cast bar, after it has solidified completely and as soon asits cross section has an [52] U.S. Cl ..29/527.6,29/527.7, 148/2,equalized temperature in the range of 9000 to 12000 C. 148/12, 164/76preferably 1,000 to l,l00 C., is shaped in one step so as to 5 l Int. Cl..B23p 25/00 reduce its cross section by about 10 to 20 percent,whereupon Fleld 0t search-w it is shorn to length, and the slabs arethen heated to rolling 164/76; 148/2, 12 temperature and shaped in aplurality of passes. Owing to this method the bubble wreath which ischaracteristic for unkilled [56] References Cited steel slabs iseliminated so that the heat transition from the i surface to the core isimproved.

UNITED STATES PATENTS 4 Claims, 1 Drawing Figure 3,317.994 5/1967Coferetal ..l64/76 PATENTEUJUL2SI9I2 3.678.571

INVENTOR. RUDOLF SCHOFFMANN ATTORNEYS METHOD FOR THE PRODUCTION OFSHEETS The invention relates to a method for the production of sheetsfrom slabs cut from a cast bar of unkilled steel which was cast by thecontinuous casting method.

There are various problems when sheets are produced from unkilled steelslabs. At first a steel has to be produced whosei oxygen content andtemperature are closely adapted to the chemical composition.Furthermore, the cross section of the bar, particularly the thickness ofthe bar, the casting speed and the cooling conditions in the continuouscasting plant are important factors which have an influence upon thequality of the product.

When unkilled steel slabs are to be processed to sheets in a train ofrolls they have to be subjected to a preliminary treatment. Theirsurface has to be examined and surface defects, have to be removed. Whenthe slabs are completely cooled,l they are heated to rolling temperaturein continuous type furnaces before they are rolled out to sheets in aplurality of passes. When the slabs are heated to rolling temperaturethe: wreath of bubbles which is characteristic for unkilled steel; slabsprovides great difficulties because it impairs the heat transition fromthe surface of the slabs into the core of the slabs when they are heatedup in gas or oil heated furnaces. As i a result, the surface isoverheated and heavy scaling occurs,

whereas the core is not sufficiently heated. This again makes forqualitative and technological disadvantages in the rollingof slabs. Theheavy scaling and overheating of the surface may lead to a connectionbetween the bubble wreath and the atmosphere which exerts an oxidizingeffect so that welding of the gas bubble hollow spaces is rendereddifficult or impossi-j ble; only waste products will be obtained whensuch a starting material is used.

ln order to avoid the difficulties which arise when heating unkilledsteel slabs because of the presence of a bubble wreath it has alreadybeen proposed to heat the slabs to rolling temperature in electricalinduction furnaces instead of in gas or oil heated furnaces. Whenelectrical induction is used, the slabs are heated more evenly overtheir entire cross section, i.e. the insulating effect of the bubblewreath does not make itself noticeable in such a disadvantageous mannerwith this kind of heating, and qualitative flaws which are unavoidablein gas or oil heated furnaces i.e. from the surface occur to a lesserdegree. However, the prime costs and the operation costs are rather highfor induction furnaces, so that for economical reasons it is ratherimprobable that induction heating for slabs will be generally used.

The thickness of unkilled steel slabs usually amounts to 250 to 300 mm;the slabs are about l,250 mm broad and up to 12 m long. Thus the crosssections and the piece weights are considerable. Attempts are being madeto find a solution for the economical and qualitative problems in therolling of unkilled steel slabs but up to now the heating problem whichpresents itself owing to the presence of the bubble wreath has remainedunsolved.

The invention is aimed at avoiding the described disadvantages anddifficulties and, in a method for the production of sheets from slabscut from a cast bar of unkilled steel which was cast by the continuouscasting method, wherein the slabs are heated to rolling temperature andshaped in a plurality of passes, resides in that the cast bar, prior tobeing shorn to length, is shaped in one step after completesolidification and' HS soon as the solidified bar has over its entirecross section a uniform temperature in the range of 900 to l,200 C.,preferably l,000 to l,l C.

Suitably, the temperature is equalized over the entire cross section ofthe bar by arranging behind the secondary cooling zone a non-cooled orheated equalization zone, respectively, through which the bar is passedprior to being shaped in one step.

Shaping according to the invention is effected to a degree which aboutcorresponds to the volume of the hollow spaces of the bubbles in the barso that the material is densified. The cross section of the bar isreduced in the one step haping process by about "to to 20 percentwithout any noticeable cogging down. Instead, re-shaping is effected.

The attached drawing shows the cross section of a bar of unkilled steelbefore being shaped according to the invention. The macroscopicstructure of a slab is schematically shown. In the bar cross sectionthree zones may clearly be distinguished, namely zone 1 which is freefrom bubbles, which zone is also called bacon layer," or skin themarginal bubble zone 2 proper, and the core zone 3 of the bar crosssection. The thickness of the marginal layer 1 which is free frombubbles in unkilled steel slabs depends on the withdrawal speed and theintensity of gas evolution and motion (boiling) of the metal in thecasting mould and in general does not amount to less than 10 mm.

When the slabs are heated to rolling temperature, it is essential tokeep the dense zone 1 as intact as possible so as to prevent oxidizinggases from entering into the marginal bubbles. When this condition isfulfilled, the marginal bubbles bond completely during rolling.

As has been mentioned, according to the invention the marginal bubblesare pressed together already when the bar is slightly shaped after itssolidification so that they are welded together and a densification ofthe bar in the area of the marginal bubble zone 2 is effected so thatthe heat insulating bubble wreath is removed. A bar of unkilled steelwhich has been densified according to this method may be heated torolling temperature in gas or oil heated furnaces exactly as a bar ofkilled steel.

The expenses for a roll stand in connection with a continuous castingplant are small. For the one step reshaping process the latent heat ofthe bar is used; the rolling pressure is rela tively small because asmall energy will suffice for pressing the hollow spaces of the bubblestogether. Owing to the fact that the bubble wreath may relatively easilybe removed the remaining zones of the bar cross section are hardlyshaped at all. Prior to carrying out the method :it is only necessary todetermine the bubble volume which depends on the steel quality and thebar cross section, but otherwise remains within narrow limits. Thus thisexamination will have to be carried out only once and then the reductionof the cross section may .be settled for the densification according tothe invention of the material.

The aim of the invention, i.e. an improvement of the quality of theslabs with regard to their heat technological properties so that anessentially improved heat transition is achieved, will also be obtainedwhen not all bubbles are welded together completely. The heating processis hardly impaired by individual bubbles which may be present stillafter shaping. Thus the method according to the invention. does notrequire high accuracy in the determination of the bubble hollow spaces,which fact simplifies its application in practice.

What 1 claim is 1. A method for the production of a steel productcomprismg,

continuously casting a steel bar,

solidifying the cast bar,

equalizing the temperature of the cast bar over its entire cross-sectionto a temperature in the range of 900-] ,200 C., reducing thecross-sectional area of the cast bar by 10 to 20 percent by means of aone-step shaping operation, shearing the bar to form individual slabs,heating the slabs to rolling temperature, and shaping and working theslabs to produce the steel product.

2. The method as defined by claim 1 wherein the cast bar is solidifiedby passing it through a cooling zone and the bar temperature isequalized by passing it through a non-cooled zone.

3. The method as defined by claim ll wherein the bar temperature isequalized by passing it through a heated zone.

4. The method as defined by claim 1. wherein the temperature of the baris equalized to approximately 1,000 to 1,100 C.

1 i i i l

1. A method for the production of a steel product comprising,continuously casting a steel bar, solidifying the cast bar, equalizingthe temperature of the cast bar over its entire cross-section to atemperature in the range of 900*-1,200* C., reducing the cross-sectionalarea of the cast bar by 10 to 20 percent by means of a one-step shapingoperation, shearing the bar to form individual slabs, heating the slabsto rolling temperature, and shaping and working the slabs to produce thesteel product.
 2. The method as defined by claim 1 wherein the cast baris solidified by passing it through a cooling zone and the bartemperature is equalized by passing it through a non-cooled zone.
 3. Themethod as defined by claim 1 wherein the bar temperature is equalized bypassing it through a heated zone.
 4. The method as defined by claim 1wherein the temperature of the bar is equalized to approximately 1,000*to 1,100* C.